Many popular beverages are available either in premixed or post-mixed form. "Premixed" in this usage means that the beverage is packaged and sold as intended for consumption, including carbonation as appropriate. With "post-mixed" beverages, in comparison, the beverage is available in a concentrate such as syrup or the like. This concentrate becomes diluted and mixed with water at the point of dispensing for consumption, and CO.sub.2 gas is then added to the mixture if the mixed beverage is carbonated. Some popular beverages are available either in premixed or post-mixed form, examples of these being cola beverages and other soft drinks. Other beverages are available only in one form; juices and other "still" or noncarbonated beverages are frequently available only as premixed beverages ready for consumption.
Soft drinks and some other premixed beverages are generally available either in bottles or cans containing only an individual serving of the beverage, or in larger bottles containing a quantity sufficient for many servings. Examples of the latter-sized bottles are the quart and multi-liter bottles of carbonated soft drinks. Neither the individual container nor the multi-serving container is entirely appropriate for many users.
For example, a consumer may simply desire less beverage than the quantity typically in individual-sized cans or bottles. The remaining beverage soon loses its carbonation and thus becomes unpalatable, even where efforts are made to reclose or reseal the container. These beverage remnants usually are discarded if not consumed very soon after the can or bottle is initially opened.
The relatively larger quart or multi-liter bottles, although typically delivered with screw-threaded caps intended for reclosure, don't adequately preserve carbonated beverages. Once the carbonation is lost when the bottle is first unsealed, the sealed pressure in the head space above the liquid no longer remains and beverage eventually becomes "flat" as the carbonation in solution in the remaining gas evolves to liquid in the empty space within the bottle.
One solution to the foregoing problem is simply to use post-mixed beverages, where the syrup or concentrate is mixed with water (and is carbonated as appropriate) when the beverage is dispensed into a cup or other container. Post-mix beverage dispensing has the added advantage that the serving portion is variable, instead of determined by the size of an individual container. Notwithstanding these and other advantages of post-mixed beverages, such dispensers generally are used only in commercial or institutional applications. The principal reasons for this limitation of use include the cost of the post-mix dispensing equipment, the relatively-large physical size of such apparatus, and the need for the apparatus to be semipermanently installed in a particular location and connected to a water line. Other disadvantages are that the user is restricted only to beverages available in concentrated form, and that both the concentrate containers and a cylinder of high-pressure CO.sub.2 gas must be periodically replenished. These and other disadvantages render post-mix beverage dispensers unattractive or undesirable in most homes, small offices, and other installations.